1. Field of the Invention
The present invention relates to an optically active compound and a ferroelectric liquid crystal composition produced therefrom which is used as a liquid crystal material for ferroelectric display devices.
More particularly, the present invention relates to a new optically active compound which has a fluorine atom introduced into the core nucleus so that it does not take on the smectic phase of a high order except for the smectic A phase and smectic C phase and which has carbonyl groups (for dipole) at adequate positions so that it exhibits greater spontaneous polarization.
The present invention also relates to a ferroelectric liquid crystal composition capable of quick response which is composed of a chiral component (including said optically active compound) and a non-chiral component.
2. Description of the Prior Art
A recent noticeable liquid crystal material for liquid crystal display devices is a ferroelectric liquid crystal which utilizes the optical switching effect produced by the chiral smectic C phase (referred to as SmC* phase hereinafter). This ferroelectric liquid crystal has several outstanding features: quick response (of the order of microseconds), bistable memory effect, easy time-sharing addressing, and wide view angle.
A ferroelectric liquid crystal has a response time which is given by the formula below. EQU .tau.=.eta./P.sub.s .multidot.E
(where P.sub.s represent the spontaneous polarization; .eta. represents the viscosity; and E represents the electric field.)
For the response time (.tau.) to be short, it is desirable that a high voltage be applied and the ferroelectric liquid crystal have a lower value of viscosity (.eta.) and a greater value of spontaneous polarization (P.sub.s).
In general, a ferroelectric liquid crystal for practical use should meet the following requirements.
(1) Great spontaneous polarization. PA0 (2) SmC* phase having a sufficiently long helical pitch, and orientation that can be easily controlled. PA0 (3) Ability to exhibit the SmC* phase over a broad temperature range (including room temperature). PA0 (4) Adequate tilt angle. PA0 (5) Chemical stability. PA0 (6) Low viscosity. PA0 (7) Bistability and a sharp threshold value.
Since there is no single material that meets all of these requirements, it is a common practice to use a mixture of two or more liquid crystals. However, none of the mixtures developed so far meet these requirements, especially (1) and (3).